The present invention relates to a method and arrangement for controlling the fuel/air ratio of an internal combustion engine in which the output voltage of an oxygen measurement probe which is arranged in the exhaust pipe of the internal combustion engine is used, after comparison with threshold values, to control the fuel/air ratio.
The oxygen measurement probes known at the present time produce an output voltage of about 0.75 V in case of a deficiency of oxygen and an output voltage of about 0.1 V in the case of an excess of oxygen. For the evaluation of the output voltage it is known to establish threshold values whereby the output voltage of the oxygen measurement probe is converted into a rectangular voltage. In the case of an aged oxygen measurement probe, the output voltage decreases, so that, for instance, only 0.55 V is present instead of 0.75 V in the case of a deficiency of oxygen. This has the result that, because of the gradual transfers in the case of an aged oxygen measurement probe a threshold value established for a voltage of 0.75 V is reached later than in the case of a new oxygen measurement probe. An impairing of the control thus results.